SENSOR AND REGULATOR PROTEINS FROM THE CYANOBACTERIUM SYNECHOCOCCUS SPECIES PCC7942 THAT BELONG TO THE BACTERIAL SIGNAL-TRANSDUCTION PROTEIN FAMILIES - IMPLICATION IN THE ADAPTIVE RESPONSE TO PHOSPHATE LIMITATION

A 1.2 kb DNA fragment was cloned from Synechococcus sp. PCC7942, which is able phenotypically to complement a phoR creC Escherichia coli mutant for the expression of alkaline phosphatase. A 2.5 kb DNA fragment encompassing the putative gene was then cloned and its complete nucleotide sequence determined. Nucleotide sequencing revealed that the intact gene encodes a protein of 46389 Da, and that the deduced amino acid sequence shows a high degree of homology to those of the bacterial sensory kinase family. In the determined nucleotide sequence, another gene was adjacently located, which encodes a protein of 29012 Da. This protein shows a high degree of homology to those of the response regulator family. Thus, we succeeded in the cloning of a pair of genes encoding the sensory kinase and response regulator, respectively, in a cyanobacterium. Mutant strains that lack these genes were constructed, and demonstrated to be defective in their ability to produce alkaline phosphatase and some inducible proteins in response to phosphate-limitation in the medium. These results imply that the gene products identified in this study are probably involved, either directly or indirectly, in the signal-transduction mechanism underlying regulation of the phosphate regulon in Synechococcus sp. PCC7942. Hence, the genes encoding the sensory kinase and response regulator were designated as sphS and sphR, respectively (Synechococcus phosphate regulon). The SphS protein was demonstrated in vitro to undergo phosphorylation in the presence of ATP.